(a) Field of the Invention
The present invention relates to a hole saw having plug ejection feature. Using the arbor and arbor nut of the present invention, the arbor of an ordinary commercially available hole saw is replaced, the arbor nut of the present invention being threaded into the hole saw cup axial threaded inlet, to convert the ordinary hole saw into a plug ejecting hole saw. The arbor and arbor nut of the plug ejecting hole saw of the present invention function as the arbor of an ordinary hole saw when used to drill the desired hole, the drill turning in a clockwise direction. When the drill rotation is reversed to a counter clockwise direction and the hole saw cup is held stationary, the arbor of the present invention screws through the also stationary arbor nut, thereby ejecting the plug from the hole saw cup.
(b) Description of the Prior Art
Hole saws, such as those designed to be used to drill "larger" circular holes, such as a 2 inch (50.8 mm) hole in a door for insertion of a lock cylinder, typically have a hole saw cup having an open cutting end with many cutting teeth, the cup having a diameter equal to the size of the hole to be cut. The cup has a base end transverse to the cup axis and opposed to the open cutting end. The base end has an axially aligned central threaded bore. This bore receives a threaded axial arbor. The arbor has an axially aligned pilot drill extending from the cup base end beyond the cup open cutting end. Typically, this is a 1/4 inch (6.35 mm) diameter drill. This pilot drill first contacts the member to be drilled, drilling a center hole which keeps the cup's open cutting end properly positioned while drilling the hole. In some hole saws, the pilot drill may extend all the way through the arbor so that the non-drilling end of the pilot drill is received into the drill with which the hole saw is used, just like any ordinary drill bit. Alternatively, the arbor may have an axially extending member which is received by the drill, the arbor securely retaining the pilot drill. For example, the arbor may have an axial bore therein with a set screw being used to retain the pilot drill in the axial bore. For a more secure fit, the pilot drill may have a flattened or chamfered portion which mates with the set screw to alleviate any tendency of the pilot drill to turn within the axial bore.
Typically, in hole saws with cups having a diameter of from 7/8 inch (22.225 mm) to 1 and 3/16 inch (30.162 mm), the cup base end axially aligned central threaded bore and the mating threaded axial arbor have a diameter of 1/2 inch (12.7 mm) with right-handed threads thereon. Typically, there are 20 threads per inch (25.4 mm). In hole saws with cups having a diameter of 11/2 inch (38.1 mm) and larger, the cup base end axially aligned central threaded bore and the mating threaded axial arbor have a diameter of 5/8 inch (15.875 mm) with right-handed threads thereon. Typically, there are 18 threads per inch (25.4 mm).
In the larger cups, drilling the larger holes, without more, the threaded connection of the arbor into the axially aligned central threaded bore receives all of the torque transferred by the drill. To alleviate this, some of the larger cups have bores into their base ends, the bores being diametrically opposed and equally spaced from the axis. The arbor can contain matching bores therein. Drive pins can then be inserted into the arbor bores and cup bores.
As a typical door is about 1 and 3/4 inch thick (44.45 mm), so that they can be used to drill completely through doors and the like, generally, hole saw cups have a depth of at least 2 inches (50.8 mm), the distance from the open cutting end to the base end. Some are deeper.
When a hole is completely drilled, for example through a door, when the cup open cutting end completes its cutting, a circular plug of cut material is retained on the pilot drill within the hole saw cup. Removal of this plug can be difficult. Some hole saw cups have openings or slits in their cup sides. The operator can try to "wiggle" the plug up out of the cup using these cup side slits. However, this can still be difficult.
U.S. Pat. No. 4,741,651, to Despres, tried to solve this problem. In Despres, a hole saw cup having left hand threads, instead of the ordinary right hand threads, in its base end threaded axial bore is taught. An arbor having a left hand threaded portion is threaded into the base end threaded axial bore. Within the hole saw cup, the threaded portion has a larger diameter flange portion thereon. This portion receives the pilot drill. Opposed to the pilot drill, the arbor has a shank portion to be received by a drill. In drilling a hole, the drill, and thus the hole saw, turn to the right, or in a clockwise direction. Therefore, the arbor will be threaded out of the cup so that the larger diameter flange portion will be forced to its closest possible location to the inside hole saw cup base end. After the hole is drilled, a pair of wrenches is used to initially break the tightened larger diameter flange portion from the hole saw cup base end. Then, if a reversible drill is used, the drill direction of rotation is reversed to counter clockwise and, holding the cup with a wrench to prevent rotation, the drill is operated to thread the arbor threaded portion up through the cup so that the plug is ejected.